Prior art electrostatographic processes are known, such as photocopying and the like in which microscopic particles are attracted to latent images in the form of discrete electrostatic charges on the surface of a suitable recording member. Such microscopic particles, usually known as toner particles, may be applied to the surface to be toned in dry powder form, or as a suspension in an insulating liquid, usually a relatively high boiling point aliphatic hydrocarbon liquid or the like.
Many methods have been proposed for the production of such toners, both dry and liquid dispersed. Toner particles in the general sense normally contain at least a pigment or dye and a binder, such as a natural or synthetic resin or polymeric material. The so-called dry toners may also have admixed therewith flow improving agents such as colloidal silica or the like to enhance their functionality in the various toner applications in use, and in addition may be mixed with so-called carrier particles, usually magnetic, which act to transport the toner to the point of application. Such carrier particles are selected to bear the correct triboelectric relationship with the toner particles to allow correct toning functionality. Normal production methods are many and varied, the most common involving hot melt mixing followed by cooling, pulverising and grinding to obtain particles of the correct particle size, normally 1 to 10 microns mean diameter. Such processes are energy inefficient and in addition environmentally unattractive due to dust generation. A further problem exists that particles produced by such processes are not necessarily spheroidal and hence do not flow well in use.
Microencapsulation techniques have also been proposed to produce more or less spherical particles, but such processes are also energy inefficient as they normally involve spray drying of water slurries of quite low solids content.
Liquid dispersed toners can generally be produced using techniques which are more energy efficient and with no significant dusting problems. However, liquid dispersed toners of the prior art normally contain other materials in addition to the colouring matter and binder resin or polymer. Such materials include surfactants, stabilisers, charge modifiers and the like, and in many instances the binder resin or polymer is partly soluble in the dispersant or carrier liquid.
It is the object of the present invention to overcome these and other problems relating to the production of both dry and liquid dispersed electrostatographic toner particles.